Refactor consensus for simulation (RIPD-1011):

This is a substantial refactor of the consensus code and also introduces
a basic consensus simulation and testing framework.  The new generic/templated
version is in src/ripple/consensus and documents the current type requirements.
The version adapted for the RCL is in src/ripple/app/consensus.  The testing
framework is in src/test/csf.

Minor behavioral changes/fixes include:
* Adjust close time offset even when not validating.
* Remove spurious proposing_ = false call at end of handleLCL.
* Remove unused functionality provided by checkLastValidation.
* Separate open and converge time
* Don't send a bow out if we're not proposing
* Prevent consensus stopping if NetworkOPs switches to disconnect mode while
  consensus accepts a ledger
* Prevent a corner case in which Consensus::gotTxSet or Consensus::peerProposal
  has the potential to update internal state while an dispatched accept job is
  running.
* Distinguish external and internal calls to startNewRound.  Only external
  calls can reset the proposing_ state of consensus

src/ripple/protocol/STValidation.h

@@ -94,7 +94,7 @@ public:
     {
         mSeen = s;
     }
-    Blob    getSigned ()                 const;
+    Blob    getSerialized ()             const;
     Blob    getSignature ()              const;
 
     // Signs the validation and returns the signing hash